This invention concerns improvements in butterfly valves for the control of gaseous fluids. Butterfly valves are useful in many industrial application, particularly large installations with high sealing requirements.
Such valves, however, require a sealing ring around the periphery of the butterfly disc. This can be achieved by use of an actuating mechanism which is not sited in the plane of the valve disc and by use of a support bridge for the spindle or shaft of the valve which is braced to the valve housing in a manner which enables the employment of a shaft which does not extend beyond the circumference of the valve disc.
As valve sizes become larger, adequate leak-proof sealing becomes more difficult, particularly when valve disc diameters reach the order of a few meters.
Nonetheless, in some industrial applications, leakage cannot be tolerated. For example, where fluids are processed which are toxic, or where gases are separated which would otherwise react, leakage of valves cannot be permitted. Additional examples can be found in the field of regenerative heat exchange and in any other regenerative process which requires switching over to other treating fluids at periodic intervals. The invention, therefore, emcompasses a butterfly valve in which means are provided to prevent leakage by supplying a purge fluid to the sealing plane between the valve seal and the seat cooperating therewith.